We have: $a^{\frac{2}{3}}=b^{\frac{2}{3}}$

Cubing both sides: $a^{2}=b^{2}$ ... Option E is correct

Dividing throughout by $b^2$: $\frac{a^{2}}{b^{2}} = 1$ ... Option C is correct


Why are options A, B and F incorrect?

We have already obtained: $a^{2}=b^{2}$

Taking square root: $|a|=|b|$

$=> a = b$ or $=> a = -b$

However, we have to choose the options that MUST be true
(Note: Options A and B may be true)

If either of $a$ and $b$ are negative (from above), their square root would become imaginary.Hence, option F is also incorrect


Answer: C and E